In recent years, it has been learnt that many of the causes of arrhythmia (or arterial fibrillation) exist within a pulmonary vein, and for this reason, if the cause of the problem is electrically isolated, arrhythmia can be cared. In accordance with this, currently popular methods of treatment adopt a metallic electrode catheter comprised of a chip of 4 mm in length to contact the ostia of pulmonary vein, where the pulmonary vein joins the left atrium, and by repeated ablation achieved using high frequency current while moving sequentially around the circular ostia of pulmonary vein, the pulmonary vein constituting the cause of arrhythmia is electrically isolated from the atrium.
However, in the above-described treatment if sequential point-contact ablation around the circular ostia of pulmonary vein is not carried out several tens of times, it is impossible to ablate the entire surroundings of each ostium; accordingly, the method in question is problematic with respect to the exceptional amount of time required. A method of proposing contact between a balloon of a high frequency current type of balloon catheter and the ostia of pulmonary vein, and ablation by high frequency current has been proposed in Japanese Patent Laid Open No. 2002-78809 as a means of achieving this treatment in a short period of time. Using this balloon catheter, there is no need to repeatedly carry out ablation in the same way as with conventional catheters, and complete circumferential ablation of the ostia of pulmonary vein is possible through a single high frequency current-carrying process; accordingly, it became possible to greatly reduce the time required for treatment while simultaneously reducing the stress placed on the patient.
When treatment of arterial fibrillation using high frequency current type of balloon catheter as explained above is carried out, it is necessary for the balloon on the distal end of the catheter to be inserted into the affected area of the heart. And in the insertion procedure, the balloon is guided to the heart via the femoral vein and the inferior vena cava; furthermore, it is introduced to the left atrium through the septum by puncturing the interatrial septum via the right atrium. Once inside the left atrium, the balloon is inflated, and wedged into the ostia of pulmonary vein. However, when this type of catheter is passed through blood vessel and heart, the balloon thereof may unintentionally interfere with vessel junctions and the interior of the heart on the way to pulmonary vein, and this has resulted in damaging the body parts such as vessels and heart. It is not always the case, therefore, that the catheter is smoothly inserted without problems occurring. Accordingly, while the balloon catheter as described above does allow ablation to be carried out in a short period of time, problems remain to be solved with regard to the insertion process.
Another problem associated with the high frequency current type balloon catheter as explained above is softening of the catheter shaft as a result of the heat generated through high frequency current-carrying. And when softening of the shaft occurs in this way, the balloon pressing against the ostia of pulmonary vein can slip away because of the influence of pulmonary venous pressure. For this reason, cooling of the interior of conventional high frequency current type of balloon catheter is carried out through the circulating coolant water. However, in order for this cooling to be achieved, a pipe for circulating the coolant water must be inserted into the catheter shaft; accordingly, the catheter shaft becomes thicker, not only impairing the handling of the catheter thereof, but also increasing the stress placed on the patient.
Furthermore, the balloon temperature of high frequency current type of balloon catheter as explained above is raised to between 50° C. and 70° C. in order for ablation to be carried out. Although temperature sensors are provided inside the balloons in order to maintain the temperature at a constant level, the balloon temperature can not be accurately measured when the configuration and structure of the temperature sensor is not correct.